This invention relates to the art of microwave generation and more specifically to the art of cyclotron maser amplifiers and oscillators in which stimulated coherent emission of microwave energy occurs by electrons in cyclotron motion in a magnetic field.
Relativistic cyclotron maser amplifiers and oscillators were originally built by Hirshfield and Wachtel as reported in "Physical Review Letters", Vol. 12, pp. 533-536 (1964), and Hirshfield's U.S. Pat. No. 3,398,376 entitled "Relativistic Electron Cyclotron Maser". The principle of operation of the Hirshfield invention is based on the stimulated emission of cyclotron radiation from free electrons in a magnetic field where such stimulated emission is possible for relativistic electrons, but not for low energy ones, wherein an electron is said to relativistic when its kinetic energy is comparable to its rest energy mc.sup.2, about 500,000 electron-volts. The device can still operate on the relativistic principle when the electron energy is less than its rest energy if the electron spends sufficient time according to the criteria, ##EQU1## where N is the number of cycles spent by the electron. The Hirshfield apparatus uses electrons of the order of 5,000 electric-volt energies resulting in a 1% relativistic increase of mass. In the art, electrons with such energies are commonly called mildly relativistic. Advanced models of the relativistic cyclotron maser typically use electrons with energies in the range of 25,000-100,000 electron-volts.
It is well known in the art, that in order for a system of free electrons in cyclotron motion to impart a net energy gain to an oscillating electromagnetic field or a wave, a phase bunching mechanism must exist. In the relativistic cyclotron maser, the phase bunching mechanism is incurred by utilizing relativistic electrons. The relativistic cyclotron frequency is ##EQU2## where V is the velocity of the electron, c is the speed of light in vacuum, and .omega..sub.c is the non-relativistic cyclotron frequency given by where e is the electron charge, B is the magnetic field strength, and m is the non-relativistic mass. When an oscillating electromagnetic field of frequency .omega..perspectiveto..omega..sub.cr is imposed on a system of relativistic electrons, electrons which lose energy will advance in phase since their frequency is increasing. Electrons that are absorbing energy are retarded in phase since their frequency is decreasing. After a number of cycles the particles become bunched, and for .omega. slightly greater than .omega..sub.cr the bunching is phased such that a net flow of energy into the oscillating electromagnetic field results.
The present invention incorporates a new physical principle of applying a static electric field of special characteristics to the electrons in cyclotron motion to induce phase bunching. The new physical principle results in the stimulated emission of cyclotron radiation by electrons which results in the stimulated emission of cyclotron radiation by electrons which are completely non-relativistic and hence, in principle, can have very low energy. This invention has significant advantages in that high electron accelerating potentials are not required. No slow-wave propagating structures are required thus allowing the use of simple and overmoded waveguides or cavity resonators. A variety of useful devices and variations based on the principles of this invention are possible.
This invention is based on the work of Larry R. Barnett for a thesis presented at the University of Tennesse, June 1978, entitled "Cyclotron Maser Instability in a Nonlinear Electrostatic Field".